1. Field of the Invention
The present invention relates to a piezoelectric resonator and an electrode structure of the piezoelectric resonator and, more particularly, to an electrode structure of a piezoelectric resonator which can be stably operated while satisfying requirements for both high reliability and low cost, and a piezoelectric resonator having the same.
2. Description of the Related Art
In general, a piezoelectric resonator has various applications, for example, in a frequency oscillator, a frequency regulator, a frequency converter, or the like. Such a piezoelectric resonator is provided using Quartz having excellent piezoelectric characteristics as a piezoelectric material, and here, Quartz serves as a stable mechanical oscillation generator.
Quartz used for piezoelectric application is artificially grown in a high pressure autoclave and cut based on a Quartz axis, and the size and shape of the Quartz to be manufactured in the form of wafer are determined in consideration of desired characteristics. Here, the Quartz is required to have low phase noise, a high quality (Q) value, and a low frequency change rate over a change in time and environment.
Here, the Q value indicates band selection characteristics in a resonator, a wave filter, an oscillator, or the like, and is also known as a coefficient of quality. The Q value is calculated as a ratio of center frequency to a 3 dB bandwidth, and as the Q value is increased, the oscillator has better frequency selection characteristics.
As an electrode structure used in a related art piezoelectric resonator, a dual-layered (or two-storied) type electrode structure has been used. Alternatively, a quadruple-layered (or four-storied) type electrode structure, including dual-layered type electrodes arranged in two rows, has been used.
As for a reduction in costs, when a piezoelectric resonator is manufactured by using a silver (Ag) electrode having good conductivity, rather than gold (Au), when an external thermal environment is changed, such as in a soldering process, an oscillation frequency of the piezoelectric resonator is changed. Such a changed frequency is recovered to the original frequency with the lapse of time. Thus, a product requiring a high precision frequency deviation such as for mobile phone radio frequency (RF) communication has previously used an Au electrode, while an Ag electrode has been used as a general purpose electrode.
In order to reduce a unit cost in the case of the use of a high-priced metal, a method for reducing the amount of Au and Ag used in electrodes by reducing the thickness thereof, or by changing a design of Quartz has been employed.
The cause of the frequency shifts due to thermal impacts on the piezoelectric resonator has not been sufficiently considered or studied to date, while Au and Ag have continued to be used as electrode materials in consideration of electrical conductivity, high mass effect, oxidization, and the like, in spite of their incurrence of a high cost.